1. Field of the Invention
This invention relates to a solid state imager device.
2. Description of the Prior Art
There has conventionally been proposed a solid state imager device as shown in FIG. 1.
In FIG. 1, there is formed on the surface of a P-type silicon substrate 1 a charge accumulating region 2 made of an N.sup.- -type region, an overflow control gate region 3 made of a P-type region adjacent to the charge accumulating region 2, and an overflow drain region 4 made of an N.sup.+ -type region adjacent to the overflow control region 3. Reference numeral 5 designates a channel stopper region, 6 a charge transfer region made of an N.sup.31 -type region, 7 a transfer electrode made of polycrystalline silicon, and 8 and 9 SiO.sub.2 layers, respectively.
The above-mentioned solid state imager device is generally referred to as a lateral overflow-structured solid state imager device. When excessive signal charges are produced due to the irradiation of intense light, they are drawn out from the charge accumulating region 2 through the overflow control gate region 3 to the overflow drain region 4 and consequently absorbed in the overflow drain region 4. Therefore, the imager device having such structure can satisfactorily remove brooming.
However, since solid state imager device of the lateral overflow structure is such that the overflow control gate region 3 and the overflow drain region 4 are juxtaposed adjacent to the charge accumulating region 2 on the surface of the P-type silicon substrate 1, a dimension or area per one pixel is increased by these regions, so that high integration of the imager device cannot be achieved.
There has also been proposed a so-called vertical overflow-structured solid state imager device as shown in FIG. 2. In such an imager device, a P-type diffusion region 11 is deposited on the surface of an N-type silicon substrate 10, and the charge accumulating region 2 made of an N.sup.31 -region is formed on the surface of the P-type diffusion region 11. When excessive signal charges are produced, they are drawn out through the P-type diffusion region 11 positioned directly below the charge accumulating region 2 to the N-type silicon substrate 10 and absorbed in the N-type silicon substrate 10. The imager device of such, vertical overflow structure can also satisfactorily remove brooming, similar to the aforementioned that of the lateral overflow structure.
However, the solid state imager device of the vertical overflow structure has difficulty in forming the P-type diffusion region 11, so that its manufacturing process is quite restricted.